In the operation of gas or combustion turbines, a hot motive gas is supplied to the turbine from a series of circumferentially disposed combustion chambers. The hot gasses flow through a transition passageway and onto a first annular blade row made up of groups of stationary blades which direct the gasses onto a subsequent row or rows of rotor blades. The rotor and typically an attached shaft are driven by the energy extracted from the hot elastic fluid, in a well known manner.
Unfortunately, the gasses provided by the several combustion chambers do not possess a uniform temperature, but rather, large temperature variations exist in both the circumferential and radial directions. Due to such unequal heating, each group of stationary blades may have different radial expansion, causing gaps allowing axial leakage. In response to such problems certain sealing systems were developed. For example, the sealing system shown in U.S. Pat. No. 3,529,906--McLaurin et al. is directed to prevent the axial flow of gas between the stator structure and the inner shroud member associated with the first row of stationary blades. The sealing system shown in U.S. Pat. No. 4,576,548 is a further attempt to resolve the leakage problem, again providing a static seal between the stator structure and the inner shroud.
While such devices have contributed toward improving the efficiency of gas turbines, a leakage problem due to axial misalignment in the turbine remains. During turbine operation a relatively significant amount of gas may leak over the outer shroud or under the inner shroud of the first row of stationary blades due to axial misalignment. Such misalignment can result from a less than perfect fit of various stator components during assembly, which fitting imperfections are amplified by thermal expansion, or from the large axial loads which are inherent in such turbines during operation. Such leakage is significant due to its effect on turbine efficiency, especially in high efficiency gas turbines where more work and higher pressure occur across the first stage than across subsequent stages. To maintain high first stage efficiency, it is important to minimize bypass leakage around the first stage stator vanes.
In prior axial flow turbines, flat radially oriented opposing surfaces were provided between the outer shroud and the turbine inner casing structure and the inner shroud and the inner liner structure for absorbing axial forces and sealing against leakage. If there were no axial misalignment present, such structure would provide an adequate seal against gas leakage. However, the presence of axial misalignment in such prior turbines resulted in either single point or two point contact between such flat surfaces, allowing leakage and a decrease in first stage efficiency.
Consequently, a need exists with regard to axial flow turbines, especially those designed for high first stage efficiency, for preventing gas leakage in the presence of axial misalignment.